The present invention relates generally to textile fabrics suitable for use in safety apparel. More particularly, the present invention relates to such fabrics which have a resistance to thermal energy from exposure to momentary electric arcs or flame.
Workers in many occupations are exposed to various personal safety hazards which can be mitigated by wearing safety apparel having selected properties such as a resistance to thermal energy from exposure to momentary electric arcs or flame. In the electric utility industry in particular, workers may be exposed to electric arcs from utility lines, transformers and other equipment, which can produce severe burn injuries and even death. Such injuries can be exacerbated if the clothing worn by an exposed worker ignites or melts from the thermal energy produced by an electric arc.
It is accordingly desirable for electric utility workers, as well as workers in other industries with similar concerns as to incidents of electric arc exposure, to wear apparel having flame resistant properties. A standard has also been promulgated by ASTM International, of West Conshohocken, Pa., formerly known as the American Society for Testing and Materials, establishing a test methodology for determining a relative rating of differing clothing materials for electric arc resistance, designated as the ASTM F1959-2004 standard. Under this testing methodology, textile fabrics are subjected to flame under defined conditions and each fabric receives a numerical rating, commonly referred to as the arc rating, that constitutes the number of calories per square centimeter the fabric will withstand when subjected to such testing. Thus, the higher a fabric's arc rating, the more resistant it has to flammability. Arc ratings are classified into four categories: Category 1 with ratings between 4 and 7.9, Category 2 with ratings between 8 and 24.9, Category 3 with ratings between 25 and 39.9, and Category 4 with ratings above 40.
Conventional wisdom in the textile fabric industry is that, in order to achieve Category 3 or Category 4 arc ratings, safety apparel fabrics must be made predominately of flame resistant or flame retardant materials, such as yarns with a relatively high content of modacrylic fiber, as modacrylic fibers are known to have good flame resistant properties. However, modacrylic fibers are also known to have low tensile strength and are also relatively expensive. Hence, flame retardant modacrylic yarns are typically made by blending modacrylic fibers with a lesser proportion of other fibers such as cotton to impart strength, producing a predominately modacrylic yarn suitable for apparel use. Generally, the industry considers that the total modacrylic content of a safety fabric must be at least 55% or greater to achieve a Category 3 arc rating.
For example, one typical conventional safety apparel fabric is made of a three-ply fleece construction utilizing three ends of yarns, each of a 55%/45% modacrylic/cotton blend to result in an overall 55% modacrylic content in the fabric as a whole. The three-ply structure of such a fabric gives it a weight suitable for various types of outerwear, e.g., sweatshirts and lightweight jackets, and when brushed or napped on one surface to raise the loft of surface fibers into a fleece-type surface, an enhanced hand and improved insulative character are imparted to the fabric. Such a fleece fabric made in a weight of about 16 ounces per square yard would typically have an arc rating of about 25, at the lowest threshold of a Category 3 range of arc ratings. Safety apparel fabrics are also known to be made in a three-ply fleece construction entirely of cotton fibers, but the fabric must be chemically treated to impregnate the entirety of the fabric with a flame resistance additive in order to achieve a moderately satisfactory arc rating within the upper end of the Category 2 range of arc ratings.
While such known fleece fabrics are usually adequate for fabrication of conventional safety apparel, a need exists within the textile industry for an alternative fabric having at least comparable physical properties (e.g., weight, strength, drapeability, hand, etc.) suitable for fabrication of safety apparel while also providing higher Category 3 or 4 arc ratings with lower cost constituent fibers.